Inheritience and Variation - Y10 Flashcards
What does DNA stand for?
Deoxyribonucleic acid
DNA: What does it do?
Contains coded info - instructions that make up an organism so it can work
Where is DNA found?
Nucleus in chromosomes
Structure of a DNA
- Double helix
- Polymer
Whats a gene?
Small section of DNA found on a chromosome
What do genes do?
Each gene codes for a particular sequence of amino acids which are put together to make a specific protein - determined by DNA too which determines what type of cell
How many amino acids are used in genes?
20 but they make up thousands of diff proteins
Whats a genome?
Entire set of genetic material in an organism
Why is the human genome important for science and medicine?
- Allows scientists to identify genes in the genome that are linked to diff types of disease
- Knowing which genes are linked to genetic diseases - helps us make effective treatments
- To trace migration -all humans descended from a common ancestor from Africa. Since ppl moved away, it caused tiny differences in the genome, by investigating these diff scientists can work out when new pops split off and what route they took
What is DNA made out of?
Nucleotides - each n has a sugar and phosphate group (forms backbone) and one “base”
What never changes in DNA?
Phosphate group and sugar molecule
4 bases, and their pairings
A - T
C- G
What is important about the DNA strands?
Complementary base pairing - A with t and C with G
How is each amino acid coded for?
By a sequence of 3 bases in a gene
What do the non coding parts do?
They dont code for proteins, they switch genes on and off, so they control whether or not a gene is expressed (used to make a protein)
Functions of proteins
- Enzymes - biological catalysts that speed up chemical reactions
- Hormones - carry msgs around body
- Structural proteins - are physically strong eg collagen
What is a mutation?
Rnaomd change in an organisms DNA which can sometimes be inherited
What do mutations do?
Change sequence of DNA bases in a gene - produces a genetic variant
How much do mutations acc make a difference?
Most have v little o no effect on the protein, some will change it a bit but function/appearance is unaffected
However, sometimes it can seriously affect a protein and make it lose its function
What happens if the enzymes actives it is changed?
Substarte may no longer bind to it
What happens if a structural protein like collagen is mutated?
Could lose their strength, making them useless
What happens if there is amutation in the non-coding DNA?
Alter how genes are expressed
3 diff types of mutations
Insertations, deletions, substitutions
What are insertations?
- New base inserted into DNA base sequence where it shouldnt be
- Changes way groups of 3 bases are read, changes amino acids that they code for
- Insertations can chnage 1+ aa as they have a knock on effect on the bases further on in the sequence
What are deletions?
- Random base is deleted from dna base sequence
- Changee the way base sequence is read, have knock on effects
What are substitutions?
- Rancom base in DNA base sequence is changed to a diff base
What is s reproduction?
2 organisms genetic info is combines = offspring which are genetically diff to either parent
How many chromosmes in each gamete?
23
What does the mixture of genetic info produce in the offspring?
Variation
What is a reproduction?
Only 1 parents so offspring is genetically identifcal to parent, clones
How does a reproduction happen?
Mitosis
Who reproduces aslly
Bacteria and some plants and animals
Advantages of s rep.
- Provides variation in the offspring - if environment changes, some offspring may survive (gives a species survival advanatge by natural selection)
Advantages of a rep.
- More efficient as 1 parent in needed, saves time and energy, faster
- Genetically identical offspring, good when conditions are favourable
Disadvantages of a rep.
- Could all die if conditions become unfavourable, since theyr’re all genetically identical
How does the malaria parasite reproduce in thhe human host? In the mosquto?
As, however inside the mosquito,parasite uses s rep.
How do fungi repdouce?
- As
- Produce spores
- Can do it s, allowing genetic variation
How do flowering plants rep.?
S, to produce seeds
However, some rep. A like strawberry
How do strawberry plants rep?
- Sends out runners
- When runner touches the soil, it can develop into a genetically indentical plant
How do daffodils rep.?
- A, by bulb division
- Parent plant has an underground bulb, produces buds
- Buds eventually for new offspring plants, genetically indentical
What is polydactyly?
- PPl have extra fingers/toes
- Caused by a dominant allele
- You cant be a carrier of the P allele
What is embryo screening?
- Embryos tested to see if they have alleles for inhertied disorders
- Embryos which dont have the defective alleles are implanted into the woman -> healthy offspring
Issues of embryo screening?
- Expensive, some think money should be spent elsewhere in the health servuce
- Large number of embryos created, small number implanted, some healthy embryos destroyed = unethical
- In future, may be able to produce offspring with desirbale features = unethical
Gene therapy
Scientists correct faulty alleles an use this to treat inhertied disorders
What is cystic fibrosis?
- Disorder of cell membranes
- Caused by recessive c
How many of the chrosome pairs contain the genes which determine inhertited characteristics only?
22, last pair determines gender
Causes of variation
- Alleles inherited
- Environment
- Genes + Environment
What causes genetic variation?
Mutations
What is evolution?
Change in the inherited characteristics of a pop over time through a process of natural selection
How have dogs been selectively bred?
To have a gentle nature
How have food crops been selectively bred?
Resistant to disease
How have animals been selectively bred?
Produce more milk/meat
How have plants been selectively bred?
Produce large or unusual flowers
How would you selective breed large cows for meat
- Take a mixed pop of cows and choose largest male and female
- Breed together
- Select largest male and female offspring and breed
- Continue doing this over many gens until all offspring are large
Problem with selective breeding
- If you breed closely related animals/plants, then we get inbreeding - prone to disease/inheritied defects
- Reuces gene pool
- If new disease appears, there is no variation so if one die, others are likely too
Process of genetic engineering
- Identify gene that you want to transfer
- Use restriction enzymes to isolate (cut) gene
- Transfer gene into a vector (virus/plasmid) depending on the type of organism that the gene is being transferred to using same restriction enzyme
- Used ligase enzyme to make sure they’re joined together
- Transfer plasmid into bacterial cell
- They multiply
plasmid comes from bacterial cell
When are genes transferred and why?
- Early stage in the organisms development (early embryo stage
- To make sure all cells receive transferred gene
- So organism development with desired characteristic
Whats genetic engineering?
Transfer a gene responsible for a desirable characteristic from one organism’s genome to another ogranism, so it also has that desired trait
4 ways genetic engineering has been used
- Bacteria has been genetically modified to produce human insulin - to treat diabetes
- Genetically modified (GM) crops have had their genes modified - to improve size, quality of fruit, make them resistant to disease, insects, herbicides
- Sheep to produce drugs in their milk to treat human diseases
- Gene therapy - inserting working genes into ppl with disease (inheritied diseases caused by faulty genes)
Long-term effects of GE
Changing an organisms genes might accidently create unplanned probs, could get passed down to future gens
Pros of GM crops
- Increase yield, more food
- Ppl in developing countries lack nutrients in their diets, GM crops could be engineered to contain missing nutrient (Golden rice is a GM crop contains beta-carotene, prevents blindness)
- Alr being grown with no probs
Cons of GM crops
- Growing GM crops will afect the number of wild flowers (so pop of insects), reducing farmland biodiversity
- Could be unsafe, ppl worried they may develop allgeries to the food, dk the effects of eating them
- Transplanted genes may get out into the natural environment eg herbicide resistance gene may be picked up by weeds, creating a new superweed variety
What is selective breeding?
Humans artifically select the plants/animals that are going to breed so genes for a particular characteristic remain in the pop, could be useful or attractive
Gene pool
number of diff alleles in a pop
2 ways plants can be cloned
Tissue culture and cuttings
How does tissue culture work?
- Divide plant into 100s of tiny pieces - has a small no of cells
- cells incubated with plant hormones - so it grows and develops
- Grow into new plants - clones of parent plant
- Made v quickly in little space, grown all year
- Used to preserve rare plants that are hard to repdocue naturally
- And by plant nurseries to produce lots of stock quickly
CONDITIONS MUST BE STERILE - NO MICROORGANISMS
How do cuttings work?
- Small piece of plant removed
- End is dipped in rooting powder - has plant hormones and encourages plant to develop roots
- genetically identical
- Produces quickly + cheaply
- Older, simple method
Process of embryo transplants
- Take sperm cell from prize bull and and egg cells from prize cow
- Sperm atifically fertilises egg cell
- Embryo develops and is split using glass rod into 2 before cells are specialised
- 2 Cloned embryos implanted into cows
Proces of adult cell cloning
- Remove cell from animal eg skin cell
- Remove nucleus
- Take unfertislied egg cell from same species from female
- Remove nucleus from egg cell
- Insert adult cell nucleus
- Give egg cell electric shock - makes egg cell divide to form an embryo
- When embryo is a ball of cells, its implanted into the womb of an adult female
Disadvantages of cloning
- Reuced gene pool - fewer diff alleles in a pop, if a pop are closely related and a new disease appears, they would all die, no allele to give resistance to it
- Cloned animals might not be as healthy as the normal ones eg Dolly the sheep had arthiritis
- Ppl worry if humans could be cloned, lead to many unsuccessful attempts and severly disabled kids
Positives of cloning
- Preserve endangered species
- Lead to greater understanding of development of the embryo, ageing and age-related disorders
Theory of evolution
Every species today have evolved from simple life forms that first started to develop over 3 bn yrs ago
How did Darwin come up with his theory?
- Observations on a round-the-world trip
- Experiments, discussions, knowledge of fossils and geology
What did Darwin conclude?
Survival of the fittest
* Organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive to reproduce and pass down these charac.
Why wasn’t Darwins theory perfect?
- Scientific knowledge wasnt availivle
- Couldn’t give a good explanation for why new chara. appeared or how organisms passed on beneficial adaptations to offspring
Explanation for variation (after Darwin)
- Phenotype controlled by genes
- New phenotpic variation occure by genetic variations caused by mutations
- Beneficial variations are passed on to future gens in genes from parents
Speciation
- Over time, the phenotype of organisms can change so much due to natural selection that a new species is formed
Reasons for extinction
- environment changes too quickly
- new predator kills
- new disease
- can compete with species for food
- catastrophic event
Why was Darwins theory controversial?
- Went against religious beliefs about how life on Earth developed, 1st plausible explanation without God (creator)
- Lack of evidence to convince scientists cuz not many other studes done into how organisms change over time
- Couldn’t explain how useful characteristics appeared or passed on, no knowledge about mutations/genes until after theory was published
What did Lamarck think?
- changes acquired during an org. lifetime is passed down
- if characteristic was used a lot, it would be more developed so offspring will inherit this
Why was Lamarck’s hypothesis rejected and not Darwins?
- Experiments didnt support this (l)
- Darwin - theory of genetics supported his idea, fossils show changes to organisms over time
Process of speciation
- Area with one species of snails
- Physical barrier separates population of snails
- Population adapt to new environment, so diff characteristics
- Diff pop wouldve changed so much they can’t reproduce together to produce fertile offspring, thus separate species
Who is Wallace?
- Scientist working at the same time as Darwin
- Early scientists working on idea of speciation
- He independaly came up with idea of natural selection and published work on the subject with Darwin is 1858
- propmted darwinin to publish “On the origin of species” in 1859
- Observations made, travelled the world, provided lots of evidence to support theory of evolution by NS
- Realised warning colours used by species to deter predators
Who was Mendel?
- Noted how characteristics in plants were passed on from one gen to the next
- Showed that height characteristics in pea plants was determined by separately inheritied “units” passed on from each parents.
Mendel’s 3 conclusions about heriditery in plants
- Characteristics in plants are determined by “heriditery units”
- Heriditery units are passed on to offspring unchanged from both parents, one unit from each
- HU can be dominant or recessive
How was Mendel’s work eventually accepted?
- Late 1800s, scientists became familiar with chromosomes - able to observe how they behaved during cell division
- Early 20th century, found out there were similiarities the way chromosomes and Mendel’s “units” acted. Found out “units” = genes found on chromosomes
- 1953, structure of DNA determined, allowed scientists to see how genes work
What are fossils?
Remains of organisms from many thousands of years ago, found in rocks
3 ways fossils are formed
- Gradual replacement by minerals
- Casts and impressions (preserved spaces eg footprints)
- Preservation in places where no decay happens
What is gradual replacement by minerals?
- Teeth, shells, bones don’t decay easily so they are replaced by minerals as they decay, forming a rock-like substance shaped like the original hard part
- Surrounding sediment turns into rock, but fossils say distinct inside the rock abd eventually smn digs it up
What are casts and impressions?
- Organism buried in soft material like clay
- Clay hardens around it and organism decays, leaving a cast of itself
- An animals burrow or plant’s roots can be preserved as casts
- Footprints can also be pressed into materials when soft, leaving an impression when it hardens
How does preservation work?
- Amber and tar pits have no oxygen/moisture so decay microbes cant survive
- In glaciers it too cold for the decay microbes to work
- Peat bogs are to acidic
Why cant scientists be certain about how life began on Earth?
- Many early life forms were soft-bodied, and soft tissue tends to decay away completely, so fossil record is incomplete
- Fossils may have been destroyed by geological activity
Why can bacteria evolve rapidly?
They reproduce at a fast rate
What causes antibiotic-resistant strains?
- Random mutations in DNA
- Causes changes in bacteria’s characteristics
Why are antibiotic-resistant strains a problem for people who become infected?
- They aren’t immune to the new strain + no treatment
- Means infection can easily spread between ppl
How is the development of new antibitiocs
- Slow and costly
- Unlikely to keep up with the emergence of new resistant strains
Ways to reduce rate of development of antibiotic strains
- Docs shouldnt prescribe antibiotics inappropriately eg for viral infections/non-serious
- Patients complete whole course so all are killed and non survive to mutate
- Agricultural use of antibiotics should be restricted
What is MRSA
- Resistant “superbug”
- Affect ppl in hospitals, fatal if it enters bloodstream
What did Carl Linnaeus propose?
Living things should be classified into groups depending on their structure and characteristics in a system
How did Linnaeus classify things?
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
What caused new models of classification to be proposed?
- Knowledge of biochemical processes taking place inside organisms developed
- Microscopes improved (info about internal structures)
What did Carl Woese propose?
- three-domain system
- Organisms are divided into archaea, bacteria, eukaryota (domains)
- These are then subdivided into smaller groups: kingdom, phylum,class,order,family,genus,species
What is archaea?
Primitive bacteria living in extreme environments
What is bacteria?
True bacteria
What is eukaryota?
Broad range of organisms: fungi, plants, protists, animals
What is the bionomial system?
- Every organism given its 2 part Latin name
- 1st part = genus - gives info on its ancestry
- 2nd part = species
- Worldwide , scientists from diff countries refer to same name - avoids confusion
What do evolutionary trees show?
- How diff species are related to each other
- Common ancestors
How do scientists work out evolutionary r/s for living organisms?
current classification data (DNA analysis, structureal similarities)
How do scientists work out evolutionary r/s for extinct organisms?
info from the fossil record
advantage of plant cloning
we know exactly the characteristics the plant will have
Do seeds produce genetically identical plants or not and why?
Offpsring would be diff, as seeds are produced by s rep
adult cell cloning vs cloning animals
adult = we know for sure as its from an adult
cloning from sperm and egg cell means we dont know for certain if characteristics will show up
What causes some parts of animals not to decay?
- If temp is too cold
- no enough o2 or water
Why do soft-bodied organisms v rarely form fossils?
- Have no skeleton
- many fossils that did form have been destroyed by changes to rocks in the crust
Process on how antibiotic resistance happens
- Mutation causes bacterium to be resistant
- antibiotic kills bacteria except resistant
- resistant survives and reproduces w/o competition
- pop of resistant strain rises and spreads
What was the first thing Linnaes did?
divided all living organisms into 2 kingdoms = animal and plant then to smaller subgroups
Do scientists now use Linnaus or Woese’s system?
3 domain system by woese - about the biochemistry eg dna and look for similarities
DNA vs RnA differences
- RNA is shorter, only a single strand, instead of thymine it has uracil
What is transcription?
Base sequence of gene is copied into mRNA (single stranded molecule)
Process of protein synthesis
- First, since the dna is too large, the base sequence needed for the protein in copied into an mRNA (transcription)
- Translation - mRNA attaches to a ribosome
- amino acids brought to ribosome on carrier molecules called tRNA
- ribosome reads triplets of bases on mRNA and uses this to join toegther the correct amino acids in the right order
- once protein chain is done, it folds into its unique shape
What does the unique shape made in protein synthesis do?
allows proteins to do theirjob as enzymes, hormones or forming structures like collagen
Why did the Theory of Evolution only gradually become accepted?
- Theory challenged idea that God made all animals/plants on earth
- insufficient evidence at the time to convince scientists
- mechanism of inheritence and variation not known until 50yrs after theory was published
2 sources that show evidence for evolution
- fossils
- antibiotic resistance in bacteria
Name everying in DNA
- made from 4 diff nucleotides,
- each has a common sugar, phosphate group with one of 4 diff bases attached to sugar
mitosis vs meiosis products
mitosis = identical
meisois = non identical
How can embryos can be screen for alleles to see a genetic disorder?
- DNA isolated from embryo
- fluorescent probe mixed with embryo DNA
- probe binds with embryo dna
- uv light to show alleles for disorder
